In commonly owned U.S. patent application Ser. No. 907,413 filed May 18, 1978 by Gunter Schulz and Konrad Klein, now U.S. Pat. No. 4,195,389, granted Apr. 1, 1980, there has been disclosed an assembly of this type comprising a plurality of cascaded drawing stages each including an elongate driven roller and a set of coacting, nondriven counterrollers. The driven rollers of these stages are rotated simultaneously at different speeds, progressively increasing from the first stage to the last, by duplicate gear trains connected to opposite ends of each driven roller in order to apply substantially identical torques to these ends for minimizing torsional stresses. It is also known to couple two coaxial roller sections to each other via a common spur gear; see U.S. Pat. No. 2,875,645.
The use of gears for the equalization of torques is inconvenient in cases where the speed ratio between the various drawing stages must be frequently changed. Such a change necessitates the replacement of certain gears which can be done only at standstill and which, moreover, may lead to errors with serious consequences as pointed out in the commonly owned patent referred to. Thus, the system described in that patent includes special torque-limiting means designed to obviate the effects of such errors of reassembly.
It has also been proposed heretofore to supplement the action of a main drive motor, coupled with a drawing roller at one end thereof, by means of an ancillary motor of lesser power driving the opposite end of that roller. This expedient, however, can only reduce but does not eliminate the torsional stresses occurring in a long roller driven only at one end.